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Standard Enthalpy Change for A Levels
Sample:
Standard Enthalpy Change of Neutralisation, ∆Hno
It is the energy evolved when one mole of water is formed during neutralisation of an acid and alkali under standard conditions
...


Terms

‘Amt of substance’
used in calculation

Sample Equation

Signs of ∆H

Remarks

∆Hno

Water formed after
neutralisation

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Always –ve

Formation of water

Standard Enthalpy Change of Neutralisation, ∆Hno
It is the energy evolved when one mole of water is formed during neutralisation of an acid and alkali under standard conditions
...
Standard Enthalpy Change of Reaction, ∆Hro
It is the energy change when molar quantities of reactants
as stated in the thermochemical equation react together
under standard conditions
...
First Ionisation Energy, I
...

It is the energy absorbed when one mole of electron is
removed from one mole of gaseous atoms to form one mole
of singly-charged gaseous cations
...
Standard Enthalpy Change of Neutralisation, ∆Hno
It is the energy evolved when one mole of water is formed
during neutralisation of an acid and alkali under standard
conditions
...
First Electron Affinity, E
...

It is the energy changed when one mole of electron is added
to one mole of gaseous atoms to form one mole of singlycharged gaseous anion
...
Standard Enthalpy Change of Combustion, ∆Hco
It is the energy evolved when one mole of a compound is
completely burnt in excess oxygen under standard
conditions
...
Standard Lattice Energy, ∆Hlatto or L
...

It is the energy evolved when one mole of an ionic
compound is formed from its constituent gaseous ions under
standard condition
...
Standard Enthalpy Change of Atomisation, ∆Hatomo

9
...
E
...


Standard Enthalpy Change of Atomisation, ∆Hatomo, of
elements
It is the energy absorbed when one mole of gaseous atoms
is formed from its element under standard conditions
...

5
...
E
...


10
...

11
...


Standard Enthalpy Change for A Levels

S/N

Terms

‘Amt of substance’
used in calculation

Sample Equation

Signs of ∆H

Remarks

1

∆Hro

Overall based on
thermochemical eqn

2H2 (g) + O2 (g) → 2H2O (l)

+/–ve

∆Hr = ∑∆Hf of product –
∑∆Hf of reactant

2

∆Hno

Water formed after
neutralisation

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Always –ve

Formation of water

3

∆Hco

Compound before
burning

C3H6 (g) + 4 O2 (g) → 3CO2 (g) + 3H2O (l)

Usually –ve

Energy is usually
released during burning

Gaseous atoms formed
after atomisation

Cl2 (g) → Cl (g)

Always +ve

Breaking the bonds
between atoms

Gaseous compound
before atomisation

C2H6 (g) → 2C (g) + 6H (g)

Always +ve

Breaking bonds in the
compound

4

∆Hatomo

5

∆Hdissoo

Covalent bonds broken
during dissociation

CH4 (g) → CH3 (g) + H (g)
Number of C-H bonds broken

Always +ve

Breaking the bond
between atoms

6

I
...


Electrons removed from
gaseous atoms

Cl (g) → Cl+ (g) + e-

Always +ve

Overcome the attraction
of valence e- and nucleus

7

E
...


Electrons added to
gaseous atoms

O (g) + e- → O- (g)

1st: Always –ve
Usually +ve

e- forms bond with atom;
overcome e- repulsion

8

∆Hlatto

Ionic compound formed
from gaseous ions

Mg2+ (g) + 2Cl- (g) → MgCl2 (s)

Always –ve

Formation of bond
between ions

9

∆Hhydo

Gaseous ions before
hydration

Na+ (g) + aq → Na+ (aq)

Always –ve

Formation of bond
between ion and water

10

∆Hsolo

Substance before
dissolving

MgCl2 (s) + aq → Mg2+ (aq) + 2Cl- (aq)

+/–ve

–ve → soluble
+ve → insoluble

11

∆Hfo

Compound formed from
K (s) + Cl2 (g) + O2 (g) → KClO3 (s)
+/–ve
∆Hfo of element = 0
constituent elements
PS: Unless the definition states that the particles are in its gaseous state, it will always be in its standard state

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